Methods and apparatuses for enabling a wireless device to communicate with a radio network node in an unlicensed spectrum

ABSTRACT

It is disclosed a wireless device ( 302, 90, 100 ), a radio network node ( 304, 70, 80 ) and methods therefore, for communicating in a network. The wireless device is configured to determine ( 52, 306 ) one or more possible first sequences of a discovery signal. The wireless device is configured to receive ( 54, 310 ) a second sequence of the discovery signal, and to determine ( 56, 312 ) if the one or more possible first sequences match the second sequence.

TECHNICAL FIELD

This disclosure relates to discovery signals in an unlicensed spectrum.In more particular, it relates to a wireless device, a radio networknode, a network system and methods therein, for enabling the wirelessdevice to communicate with the radio network node in the unlicensedspectrum.

BACKGROUND

As the number of wireless devices increases, there is an endeavour toincrease resource utilization in radio frequency spectrum.

Licensed radio frequency spectrum, for which long term evolution (LTE)is designed, provides many benefits in terms of network planning andquality-of-service guarantees, in relation to an unlicensed radiofrequency spectrum. Since the amount of licensed spectrum is limited andhas a price in terms of license cost, many operators exploit unlicensedspectrum, which comes at no licensing cost, as a complement in order tooffload the LTE networks. In most cases, WiFi based on the IEEE 802.11family of technologies is the technology used. Although WiFi providesmeans to access unlicensed spectrum, it has several drawbacks such aslimited support for mobility and quality-of-service handling Recently,the interest in using LTE for accessing unlicensed spectrum hasincreased.

Carrier aggregation, where a wireless device receives or transmits onmultiple component carriers, is an integral part of LTE from release 10onwards. In the LTE specifications, the component carriers correspond toa primary cell (PCell) and secondary cells (SCells).

From the perspective of the wireless device, there is only one PCell,whereas there may be one or more SCells. Cross-carrier scheduling isalso supported, in which case downlink assignments and uplink schedulinggrants relating to one carrier, e.g. an SCell, may be sent on anothercarrier, e.g. the PCell, using the (enhanced) physical downlink controlchannel ((E)PDCCH). Similarly, uplink control signalling on physicaluplink control channel (PUCCH) from a user equipment (UE) to an evolvedNodeB (eNodeB) is transmitted on the PCell regardless of whether itrelates to the PCell or a SCell.

One possibility for accessing unlicensed spectrum with LTE is to buildon the carrier aggregation framework already part of LTE, where theprimary carrier corresponding to a PCell operates in a licensed spectrumwhereas one or more secondary carriers corresponding to one or moreSCells operate in an unlicensed spectrum.

The PCell is used for all mobility procedures, handles all criticalcontrol signalling, as well as user data, whereas the one or more SCellsare used for best effort user data. This approach allows exploiting theunlicensed spectrum for LTE users without scarifying mobility andquality-of-service support. In addition, the operator only needs tohandle one network.

An alternative to carrier aggregation is dual connectivity frameworkcurrently being developed in 3GPP, for multiple component carriers. Indual connectivity the carriers are associated with different basestations. Dual connectivity applied to licensed and unlicensed spectra,provides flexibility as the licensed and unlicensed accesses areimplemented in separate nodes.

This is in contrast to carrier aggregation, where a PCell and a SCellare co-located in the same network node or base station.

Before an LTE wireless device may communicate with an LTE radio networknode, the wireless device has to find and acquire synchronization to acell within the LTE network and determine the identity of the cellfound. This process is known as cell search. To assist the wirelessdevice in this process, LTE defines two signals, the primary andsecondary synchronization signals (PSS and SSS), which are transmittedfrom every LTE cell. The PSS/SSS are transmitted regularly every 5 ms.By measuring on these signals, the wireless device may establish timeand frequency synchronization with the cell. Furthermore, differentcells use different sequences and the wireless device may thereforeestablish the physical-layer cell identity by observing which PSS andSSS sequence in the set of possible sequences the cell in question used.Once synchronization to a cell is obtained, the wireless device mayreceive system information transmitted by each cell to obtaininformation necessary for accessing the system. The system informationcontains the so-called public land mobile network identity (PLMN ID),which is a globally unique identity of the operator to which the cellbelongs. The PSS/SSS pair to use in a specific cell is determined by theoperator as part of the network planning. Since LTE operates in licensedspectrum, the same set of PSS/SSS sequences may be used by multipleoperators as they are assigned different carrier frequencies.

For operation in unlicensed spectrum, as well as part of generalenhancements to LTE in other areas such as coordinated multipointtransmission and reception (CoMP), so-called discovery signals arediscussed.

A discovery signal is a sequence or set of sequences, typically oforthogonal frequency division multiplexing (OFDM) symbols, which aretransmitted infrequently, e.g. a few times per second, from atransmission point, or a radio network node. A discovery signal maycomprise un-modulated tones transmitted on a sequence of OFDM symbols.

By searching for discovery signals, a wireless device may find thetransmission point and report e.g. the received signal quality to thenetwork, which may use this information to determine whether thetransmission point should be used for transmission to that wirelessdevice or not.

In case of operation in unlicensed spectrum, each radio network nodethat transmits in unlicensed spectrum also transmits a discovery signal.Based on wireless device measurements on observed discovery signals, theradio network node may determine whether the wireless device shouldreceive transmissions from a SCell that is operating in unlicensedspectrum.

The radio network node may configure the wireless device to search for aparticular set of discovery signals. Alternatively, the wireless devicesearches over the full set of discovery signals without receivinginformation from the radio network node about the subset of discoverysignals to search for. Upon detection of a discovery signal, thewireless device may report the signal quality back to the cell to whichit is connected, after which the radio network node may, based uponthis, take the desired action.

Transmissions in LTE are fully scheduled, i.e. a radio network node,such as an eNodeB is in control of when and on what resources wirelessdevice, such as a UE shall be transmitting.

FIG. 1 schematically presents a network 16, in which a UE, 12 is servedby an eNodeB 14.

In contrast to LTE, transmissions in WiFi are not scheduled but areautonomously handled.

FIG. 2 presents a scheme for transmission in WiFi, illustrating a firstnode 20, and a second node, 22 attempting unscheduled transmission. Whenthe first node 20 has data to transmit, it listens to the channelactivity for a certain amount of time, for example 20 microseconds (μs),and assesses whether the channel is available for transmission. Sincethe second node 22 is not transmitting any data during the listeningtime of the first node 20, the first node, 20 assesses that the channelis available for transmission, and may thus start transmission on thechannel.

If the second node 22, assesses the channel availability duringtransmission by the first node 20, the second node 22 assesses that thechannel as not available for uplink transmission. The second node 22then waits a “back-off duration” in time, after which it assesses thechannel availability again. Since the first node 20 does not transmitany data during this time, the second node 22 declares the channelavailable for transmission, after which it may transmit uplink data.

The scheme as presented in FIG. 2 is called listen before talk (LBT)since a node has to listen to the channel and assess the availabilitybefore it may transmit, i.e. talk. The use of LBT allows WiFi devices toshare the spectrum among a multiple of other WiFi nodes. Moreover, theLBT allows WiFi devices to share the spectrum among non-WiFi devices.

There may also be regulatory requirements on LBT or similar schemes insome bands and regions.

When extending LTE to access an unlicensed spectrum on a SCell, it maybe beneficial and may become a requirement to support LBT. In thedownlink, the eNodeB may listen on the channel prior to the start of asubframe and, if the channel is declared available, schedule datatransmissions in the subframes following the listening period.

The same principle may be applied in the uplink. If the UE finds thechannel available, it follows the scheduling grant from the eNodeB andtransmits in the uplink, otherwise it ignores the grant.

Preferably, the LBT period for all UEs connected to the same unlicensednode overlap as transmissions within that SCell are coordinated throughscheduling. Uplink transmission should be avoided only when other nodes(e.g. WiFi) are currently using the channel.

Multiple operators may use the same unlicensed spectrum. Unless someother inter-operator coordination mechanism is used, the LBT periodbetween different operators should in this case preferably not overlapas there is no scheduling coordination between the different operators.From one operator's perspective, another operator using LTE inunlicensed spectrum is no different from another operator using WiFi inunlicensed spectrum. A similar problem may also arise for differentnodes belonging to the same operator if these nodes are not tightlycoordinated.

In unlicensed spectrum, determining a discovery signal sequence inunlicensed spectrum cannot rely on network planning since multipleoperators may use the same standard and hence the same overall set ofpossible sequences in the same spectrum. This is in contrast totraditional PSS/SSS configuration, for cell planning, in licensedspectrum, where only one operator exists on each frequency in a givengeographical area.

Also, linking the discovery signal sequence to use in a particularnetwork node to the globally unique PLMN ID may not be a good ideaeither, as the set of possible sequences becomes very large due to thelarge number of possible PLMN IDs.

There is hence a need for a solution addressing these issues asdiscussed above.

SUMMARY

It is an object of exemplary embodiments to address at least some of theissues outlined above, and this object and others are achieved by awireless device, a radio network node and methods therein, according tothe appended independent claims, and by embodiments of the exemplaryembodiments according to the dependent claims.

According to an aspect, the exemplary embodiments provide a method in awireless device for communicating with a radio network node. Within themethod the radio network node serves a first cell in a licensed spectrumand a second cell in an unlicensed spectrum. The method comprisesdetermining at least one first sequence of a discovery signal, based oncarrier frequency information of the first cell. The method alsocomprises receiving a second sequence of the discovery signal in thesecond cell. In addition, the method comprises determining if said atleast one first sequence match the second sequence.

According to another aspect, the exemplary embodiments provide a methodin a radio network node for communicating with a wireless device. Withinthe method the radio network node serves a first cell in a licensedspectrum and a second cell in an unlicensed spectrum. The methodcomprises determining at least one first sequence of a discovery signalfor the wireless device based on carrier frequency information of thefirst cell. In addition, the method comprises transmitting the sequenceof the discovery signal in the second cell.

According to yet another aspect, the exemplary embodiments provide awireless device that is adapted to communicate with a radio networknode. The wireless device comprises a receiver, and a processing unit.The processing unit is adapted to determine at least one first sequenceof a discovery signal, based on carrier frequency information of thefirst cell. The processing unit is further adapted to receive via thereceiver a second sequence of the discovery signal in a second cell. Inaddition, the processing unit is further adapted to determine if said atleast one first sequence match the second sequence.

According to still yet another aspect, the exemplary embodiments providea radio network node that is adapted to communicate with a wirelessdevice. The radio network node comprises a transmitter, and a processingunit. The processing unit is adapted to determine a sequence of adiscovery signal for the wireless device based on carrier frequencyinformation of a first cell in a licensed spectrum. In addition, theprocessing unit is adapted to transmit via the transmitter the sequenceof the discovery signal in a second cell in an unlicensed spectrum.

According to yet another aspect, the exemplary embodiments provide amethod in a network system comprising a radio network node serving afirst cell in a licensed spectrum and a second cell in an unlicensedspectrum and further comprising a wireless device the method comprising:determining by said radio network node a sequence of a discovery signalfor the wireless device based on carrier frequency information of thefirst cell; transmitting by said radio network node the sequence of thediscovery signal in the second cell in the unlicensed spectrum;determining by the wireless device at least one first sequence of adiscovery signal, based on the carrier frequency information of thefirst cell receiving by the wireless device from the radio network nodethe second sequence of the discovery signal in the second cell; anddetermining by the wireless device if said at least one first sequencematches the second sequence.

The exemplary embodiments provide discovery signals in an unlicensedspectrum, and enable wireless devices to determine if a discovery signalin an unlicensed spectrum is associated with the operator of thewireless device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail, and with reference tothe accompanying drawings, in which:

FIG. 1 schematically illustrates a communication network;

FIG. 2 schematically illustrates resource availability check in priorart;

FIG. 3 presents a handshake diagram of signalling according toembodiments of the exemplary embodiments;

FIGS. 4 and 5 illustrate flow-charts of methods according to embodimentsof the exemplary embodiments;

FIG. 6 schematically illustrates cells in unlicensed spectrum withincells in licensed spectrum according to embodiments of the exemplaryembodiments;

FIGS. 7 and 8 schematically present a radio network node according toembodiments of the exemplary embodiments; and

FIGS. 9 and 10 schematically present a wireless device according toembodiments of the exemplary embodiments.

DETAILED DESCRIPTION

In the following description, different embodiments of the exemplaryembodiments will be described in more detail, with reference toaccompanying drawings. For the purpose of explanation and notlimitation, specific details are set forth, such as particular examplesand techniques in order to provide a thorough understanding.

Determination of and use of discovery signal sequence(s) in unlicensedspectrum cannot rely on network planning. This is because multipleoperators may use the same standard, which could result in the same setof discovery signal sequences being used by two or more operators.

There is therefore a need to enable wireless devices to determine if asignal sequence of a discovery signal is associated with the operator ofthe wireless device.

By determining a sequence of a discovery signal, based on a quantitythat is unique to a cell in a licensed spectrum of an operator, awireless device may determine if a received sequence of the discoverysignal is a sequence from the operator of the wireless device.

As will be described further down, the determination of a discoverysignal sequence may also be based on a physical—layer cell identity (ID)of the cell in the licensed spectrum.

FIG. 3 presents a handshake diagram of signaling between a wirelessdevice 302 and a radio network node 304, for enabling communicationbetween the wireless device 302 and the radio network node 304. Theradio network node 304 serves a first cell in a licensed spectrum and asecond cell in an unlicensed spectrum.

In 306, the wireless device 302 determines at least one first sequenceof a discovery signal, based on carrier frequency information of thefirst cell. The wireless device has prior knowledge of the carrierfrequency of the first cell.

Since a carrier frequency of the first cell is unique for the operator,the at least one first sequence will be associated with the operator ofthe wireless device. By determining one or more first sequences, thewireless device determines one or more possible sequences of a discoverysignal associated with the operator.

In 308, the radio network node 304 determines a sequence of thediscovery signal for the wireless device, based on the carrier frequencyinformation of the first cell. The sequence as determined by the radionetwork node is in FIG. 3 denoted a “second” sequence.

In 310, the radio network node 304 transmits the second sequence of thediscovery signal in the second cell in the unlicensed spectrum.

In 312, the wireless device 302 determines if said at least one firstsequence match the second sequence. The wireless device thus determinesif any of the possible first sequences match the second sequence asreceived from the radio network node. The wireless device may thusdetermine a first sequence in the unlicensed spectrum, which firstsequence is associated with the operator of the first cell in thelicensed spectrum.

FIG. 4 presents a flow chart of a method in a radio network node forcommunicating with a wireless device. Within the method the radionetwork node serves a first cell in a licensed spectrum and a secondcell in an unlicensed spectrum. The method comprises determining 42 asequence of a discovery signal for the wireless device based on carrierfrequency information of the first cell. In addition, the methodcomprises transmitting 44 the sequence of the discovery signal in thesecond cell.

Determining 42 the sequence of the discovery signal, within the methodin the radio network node, may be based on a function dependent on thecarrier frequency information of the first cell.

Determining 42 the sequence of the discovery signal for the wirelessdevice, within the method in the radio network node, may be based onphysical layer cell identity information of the first cell.

FIG. 5 presents a flow chart of a method in a wireless device forcommunicating with a radio network node. Within the method the radionetwork node serves a first cell in a licensed spectrum and a secondcell in an unlicensed spectrum. The method comprises determining 52 atleast one first sequence of a discovery signal, based on carrierfrequency information of the first cell. The method also comprisesreceiving 54 a second sequence of the discovery signal in the secondcell. In addition, the method comprises determining 56 if said at leastone first sequence match the second sequence.

Determining 52 the at least one first sequence of the discovery signal,within the method in the wireless device, may be based on a functiondependent on the carrier frequency information of the first cell. Anexample of a function may be a two-dimensional table having at least twocolumns, one column comprising PCell frequency information and the othercolumns corresponding discovery signal sequence information as explainedbelow. For such a function, for each PCell-frequency information a listof discovery signal sequence(s) that may be used may be defined. Anotherexample of a function may be to define a discovery signal index as:“discovery single index=PCell-frequency mod N” were mod stands formodulo operation and N is the number of possible discovery signals orthe number of possible discovery signal sequences.

The method in the wireless device may further comprise receivingphysical layer cell identity information of the first cell, anddetermining 52 the at least one first sequence of the discovery signal,may be based on the received physical layer cell identity information ofthe first cell.

Determining 56 if said at least one first sequence match the secondsequence, within the method in the wireless device, may comprise mappingthe at least one first sequence with the second sequence.

The determination of the discovery signal sequence or sequences a givensecond cell operating in unlicensed spectrum should use may be based ona function taking as input a quantity of the first in licensed spectrum,which quantity differs between operators. For example, the discoverysignal to use could be based on the carrier frequency of the first cellalone, or on the carrier frequency of the first cell and thephysical-layer cell ID of the first cell.

These two alternatives ensure that different operators using the sameunlicensed spectrum may be assigned different discovery signals.

One possibility to organize a set of possible discovery signal sequencesis to divide them into groups with one of or more signals in each group.Denote the discovery signal sequence transmitted by a particular node asCij where i is a group number and j the number of the sequence withingroup i. The number i is then determined as a function of the quantitythat differ between operators, as mentioned above. The number j may beselected freely by the operator, if there are more than one discoverysignal sequence in the group i.

TABLE 1 Example of possible grouping of discovery signal sequences Cij j= p j = q j = r i = k  Ckp Ckq Ckr i = m Cmp Cmq Cmr

Including the physical-layer cell identity in the discovery signalselection is beneficial when a cell using unlicensed spectrum at leastto some degree overlaps multiple other cells in licensed spectrum.

FIG. 6 schematically illustrates an example in which cells in unlicensedspectrum within other cells in licensed spectrum according toembodiments of the exemplary embodiments.

In FIG. 6 cell 610 having discovery signal sequence Ckr, is used inaggregation with a licensed cell A, 602 partially overlaps licensed cellB, 604. If the discovery signal sequence Ckr is used also by cellsoperating in aggregation with cell B, 604, the network cannotdistinguish between cases where the unlicensed cell 610 should not beincluded in a carrier aggregation setup and when it should.

Basing discovery signal selection on the carrier frequency of a cell ina licensed spectrum may thus not be sufficient. Neither would it besufficient to base the discovery signal selection on a PLMN ID alone.

Therefore discovery signal selection may in addition be based on thephysical-layer cell identity of the cell in the licensed spectrum, withwhich the second cell may be aggregated with.

Multiple sequences in a group is useful if an operator has multipleunlicensed cells nodes operating in aggregation with the same licensedcell. One example is cells 606 and 608, having discovery signals Ckp andCkq, respectively, in FIG. 6. Another example is cells 612 and 614,operating in aggregation with licensed cell B, 604, having discoverysignal sequences Cmp and Cmq, respectively.

FIG. 7 schematically presents a radio network node 70 for acommunicating with a wireless device. The radio network node 70comprises a transmitter 72, and a processing unit 74. The processingunit is adapted to determine 42 a sequence of a discovery signal for thewireless device based on carrier frequency information of a first cellin a licensed spectrum. In addition, the processing unit 74 is adaptedto transmit 44 via the transmitter 72 the sequence of the discoverysignal in a second cell in an unlicensed spectrum.

The processing unit 74 of the radio network node 70 may comprise aprocessor and a memory and wherein said memory contains instructionsexecutable by said processor.

The processing unit 74 of the radio network node 70 may further beadapted to determine 42 the sequence of the discovery signal, based on afunction dependent on the carrier frequency information of the firstcell.

The processing unit 74 of the radio network node 70 may further beadapted to determine 42 the sequence of the discovery signal for thewireless device based on physical layer cell identity information of thefirst cell.

The radio network node 70 may be configured to serve the first cellbeing a primary cell, PCell, and may be configured to serve the secondcell being a secondary cell, SCell.

The radio network node 70 may comprise an eNodeB.

FIG. 8 schematically presents a radio network node 80 for acommunicating with a wireless device. The radio network node 80comprises determining means 82 and transmitting means 84. Thedetermining means 82 is adapted to determine 42 a sequence of adiscovery signal for the wireless device based on carrier frequencyinformation of a first cell in a licensed spectrum. The transmittingmeans 84 is adapted to transmit 44 the sequence of the discovery signalin a second cell in an unlicensed spectrum.

FIG. 9 schematically presents a wireless device 90 that is adapted tocommunicate with a radio network node 70, 80. The wireless device 90comprises a receiver 92, and a processing unit 94. The processing unit94 is adapted to determine 52 at least one first sequence of a discoverysignal, based on carrier frequency information of the first cell. Theprocessing unit 94 is further adapted to receive 54 via the receiver 92a second sequence of the discovery signal in a second cell. In addition,the processing unit 94 is further adapted to determine 56 if said atleast one first sequence match the second sequence.

The processing unit 94 of the wireless device 90 may comprise aprocessor and a memory and wherein said memory contains instructionsexecutable by said processor.

The processing unit 94 of the wireless device 90 may further be adaptedto determine 52 the at least one first sequence of the discovery signal,based on a function dependent on the carrier frequency information ofthe first cell.

The processing unit 94 of the wireless device 90 may further be adaptedto receive via the receiver 92 physical layer cell identity informationof the first cell. The processing unit 94 may further be adapted todetermine 52 the at least one first sequence of the discovery signal,based on the received physical layer cell identity information of thefirst cell.

The processing unit 94 of the wireless device 90 may further be adaptedto map the at least one first sequence with the second sequence.

The wireless device may comprise a UE.

FIG. 10 schematically presents a wireless device 100 that is adapted tocommunicate with a radio network node 70, 80. The wireless device 100comprises determining means 102 and receiving means 104. The determiningmeans 102 is adapted to determine 52 at least one first sequence of adiscovery signal, based on carrier frequency information of the firstcell. The receiving means 104 is adapted to receive 54 a second sequenceof the discovery signal in a second cell. In addition, the determiningmeans 102 is adapted to determine 56 if said at least one first sequencematch the second sequence.

Hence, according to some exemplary embodiments, there is provided amethod in a network system comprising a radio network node serving afirst cell in a licensed spectrum and a second cell in an unlicensedspectrum and further comprising a wireless device the method comprising:

determining by said radio network node a sequence of a discovery signalfor the wireless device based on carrier frequency information of thefirst cell; transmitting by said radio network node the sequence of thediscovery signal in the second cell in the unlicensed spectrum;determining by the wireless device at least one first sequence of adiscovery signal, based on the carrier frequency information of thefirst cell receiving by the wireless device from the radio network nodethe second sequence of the discovery signal in the second cell; anddetermining by the wireless device if said at least one first sequencematches the second sequence.

Embodiments herein may be applicable to cases in which there are two ormore carriers. Two examples of frameworks for using two or more carriersare carrier aggregation and dual connectivity.

Carrier aggregation is an integral part of LTE. In current LTEspecifications, the component carriers correspond to a PCell (PrimaryCell) and one or more SCells (Secondary Cells).

In carrier aggregation, the PCell and the one or more SCells areco-located in the same radio network node.

In dual connectivity, two carriers are associated with separate radionetwork nodes.

For dual connectivity as a frame work for license-assisted access tounlicensed spectrum, the nodes operating in unlicensed spectrum mayreceive information about which discovery signals to transmit over theX2 interface from a radio eNodeB operating in licensed spectrum in thesame area. Alternatively, the sequence may be set directly by theoperator through the operation and maintenance (O&M) system.

Carrier aggregation or dual connectivity may be combined with exploitingan unlicensed spectrum. In carrier aggregation, the PCell will thencorrespond to the licensed spectrum, and the one or more SCells willcorrespond to an unlicensed spectrum.

Using dual connectivity provides additional flexibility as licensedaccess and unlicensed access are implemented in separate nodes.

Although embodiments may be described using an emphasis on carrieraggregation framework, the dual connectivity framework may be usedequally well.

Above, the exemplary embodiments have been described in the context ofdetermining an operator specific discovery signal sequence to use.However, the principle may be used when determining other parameterswhich should preferably differ between different operators, for instancethe LBT time instant in a cell when operating in unlicensed spectrum.

It is noted that operator specific LBT periods between cells in asynchronized network may be achieved by linking the listening instant tothe PLMN ID, but also in this case the linkage may become cumbersome asthere is a large number of possible PLMN IDs. Furthermore, an operatorwith a specific PLMN ID may or may not want the LBT instants to overlapbetween nodes belonging to said operator, in which case a PLMN-IDlinkage is less desirable.

With the described embodiments herein the following advantages may beachieved: Providing discovery signals in an unlicensed spectrum andenabling wireless devices to determine if a discovery signal in anunlicensed spectrum is associated with the operator of the wirelessdevice. Thus, the exemplary embodiments provide different operatorsusing the same unlicensed spectrum different discovery signals.License-assisted access to unlicensed spectrum is thus enabled.

It may be further noted that the above described embodiments are onlygiven as examples and should not be limiting to the present exemplaryembodiments, since other solutions, uses, objectives, and functions areapparent within the scope of the embodiments as claimed in theaccompanying patent claims.

ABBREVIATIONS

3GPP 3^(rd) generation partnership project

CoMP coordinated multi point transmission and reception

(E)PDCCH (enhanced) physical downlink control channel

ID identity

LBT listen before talk

LTE long term evolution

O&M operation & maintenance

OFDM orthogonal frequency division multiplexing

PCell primary cell

PLMN public land mobile network

PSS primary synchronization signal

PUCCH physical uplink control channel

SCell secondary cell

SSS secondary synchronization signal

UE user equipment

The invention claimed is:
 1. A method in a wireless device forcommunicating with a radio network node, the radio network node servinga first cell in a licensed spectrum and a second cell in an unlicensedspectrum, the method comprising: determining one or more first possiblesequences for discovery signals expected to be transmitted by cellsassociated with the first cell but transmitting in unlicensed spectrum,based on carrier frequency information of the first cell; receiving adiscovery signal in the second cell, in the unlicensed spectrum, thereceived discovery signal comprising a received sequence; determiningwhether the received sequence matches any of the one or more firstpossible sequences; and upon determining that the received sequencematches any of the one or more first possible sequences, reporting oneor more measurements for the received discovery signal to the radionetwork node.
 2. The method of claim 1, further comprising determiningthe one or more first possible sequences for the discovery signals basedon a function dependent on the carrier frequency information of thefirst cell.
 3. The method of claim 1, further comprising receivingphysical layer cell identity information of the first cell, anddetermining the one or more first possible sequences for the discoverysignals based on the received physical layer cell identity informationof the first cell.
 4. The method of claim 1, wherein determining whetherthe received sequence matches any of the one or more first possiblesequences comprises mapping each of the one or more possible firstsequences with the received sequence.
 5. A method in a radio networknode for communicating with a wireless device, the radio network nodeserving a first cell in a licensed spectrum and a second cell in anunlicensed spectrum, the method comprising: determining a sequence for adiscovery signal, for transmitting by the second cell to the wirelessdevice in the unlicensed spectrum, wherein said determining is based oncarrier frequency information of the first cell; and transmitting thediscovery signal in the second cell, in the unlicensed spectrum, thetransmitted discovery signal comprising the determined sequence.
 6. Themethod of claim 5, further comprising determining the sequence of thediscovery signal based on a function dependent on the carrier frequencyinformation of the first cell.
 7. The method of claim 5, furthercomprising determining the sequence of the discovery signal for thewireless device based on physical layer cell identity information of thefirst cell.
 8. A wireless device adapted to communicate with a radionetwork node, the wireless device comprising: a receiver; and aprocessing unit circuit configured to: determine one or more firstpossible sequences for discovery signals expected to be transmitted bycells associated with the first cell but transmitting in unlicensedspectrum, based on carrier frequency information of the first cell;receive via the receiver a discovery signal in the second cell, in theunlicensed spectrum, the received discovery signal comprising a receivedsequence; determine whether the received sequence matches any of the oneor more first possible sequences; and report one or more measurementsfor the received discovery signal to the radio network node, upondetermining that the received sequence matches any of the one or morefirst possible sequences.
 9. The wireless device of claim 8, wherein theprocessing circuit is further configured to determine the one or morefirst possible sequences based on a function dependent on the carrierfrequency information of the first cell.
 10. The wireless device ofclaim 8, wherein the processing circuit is further configured to receivevia the receiver physical layer cell identity information of the firstcell, and wherein the processing circuit is further configured todetermine the one or more first possible sequences based on the receivedphysical layer cell identity information of the first cell.
 11. Thewireless device of claim 8, wherein the processing circuit is furtherconfigured to map each of the one or more first possible sequences withthe received sequence.
 12. A radio network node adapted to communicatewith a wireless device, said radio network node comprising: atransmitter; and a processing circuit configured to: determine asequence for a discovery signal, for transmitting by a second cell tothe wireless device in an unlicensed spectrum, wherein said determiningis based on carrier frequency information of a first cell in a licensedspectrum; and transmit via the transmitter the discovery signal in thesecond cell in the unlicensed spectrum, the transmitted discovery signalcomprising the determined sequence.
 13. The radio network node of claim12, wherein the processing circuit is further configured to determinethe sequence of the discovery signal based on a function dependent onthe carrier frequency information of the first cell.
 14. The radionetwork node of claim 12, wherein the processing circuit is furtherconfigured to determine the sequence of the discovery signal for thewireless device based on physical layer cell identity information of thefirst cell.
 15. The radio network node of claim 12, being configured toserve the first cell being a primary cell (PCell) and further beingconfigured to serve the second cell being a secondary cell (SCell). 16.A method in a network system comprising a radio network node serving afirst cell in a licensed spectrum and a second cell in an unlicensedspectrum and further comprising a wireless device, the methodcomprising: determining by said radio network node a sequence for adiscovery signal, for transmitting by the second cell to the wirelessdevice in the unlicensed spectrum, wherein said determining is based oncarrier frequency information of the first cell; transmitting by saidradio network node the discovery signal in the second cell, in theunlicensed spectrum, the transmitted discovery signal comprising thedetermined sequence; determining by the wireless device one or morefirst possible sequences for discovery signals expected to betransmitted by cells associated with the first cell but transmitting inunlicensed spectrum; receiving by the wireless device from the radionetwork node a discovery signal in the second cell, in the unlicensedspectrum, the received discovery signal comprising a received sequence;determining by the wireless device whether the received sequence matchesany of the one or more first possible sequences; and reporting by thewireless device one or more measurements for the received discoverysignal to the radio network node, upon determining that the receivedsequence matches any of the one or more first possible sequences.